Vaccines have been one of the great public health inventions of modern medicine and have saved millions of lives. Immunizations have been proven to be an ideal means to prevent and control infections. Each year vaccines prevent up to 3 million deaths and 750,000 children are saved from disability. (Global Alliance for Vaccines and Immunization—Press Releases (Mar. 11, 2006) at www.gavialliance.org/media_centre/press_releases/2006_03_09_en_pr_queenrania_delhi.php). In 1999 the CDC declared immunizations the number one public health achievement of the 20th century (Ten great public health achievements-United States, 1900-1999. MMWR Morb Mortal Wkly Rep 48:241-3 (Apr. 2, 1999)). Some bacteria like those causing tetanus or diphtheria produce a toxin that is largely responsible for the disease. This toxin can be used in a detoxified form as vaccine. However, for most bacteria there is no single toxin that can be used to develop a vaccine.
Among the most successful vaccines are surface polysaccharides of bacterial pathogens like Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae conjugated to carrier proteins. These bacteria are surrounded by a capsule, which promotes microbial virulence and resistance to phagocytic killing, as well as preventing them from desiccation.
Bacterial polysaccharides can elicit a long-lasting immune response in humans if they are coupled to a protein carrier that contains T-cell epitopes. This concept was elaborated 80 years ago (Avery, O. T., and W. F. Goebel. 1929. Chemo-immunological studies on conjugated carbohydrate-proteins. II Immunological specificity of synthetic sugar-proteins. J. Exp. Med. 50:521-533), and proven later for the polysaccharide of Haemophilus influenza type B (HIB) coupled to the protein carrier diphtheria toxin (Anderson, P. 1983. Antibody responses to Haemophilus influenzae type b and diphtheria toxin induced by conjugates of oligosaccharides of the type b capsule with the nontoxic protein CRM197. Infect Immun 39:233-8; Schneerson, R., O. Barrera, A. Sutton, and J. B. Robbins. 1980. Preparation, characterization, and immunogenicity of Haemophilus influenzae type b polysaccharide-protein conjugates. J Exp Med 152:361-76). This glycoconjugate was also the first conjugated vaccine to be licensed in the USA in 1987 and introduced into the US infant immunization schedule shortly thereafter. Besides HIB, conjugated vaccines were successfully used against the encapsulated human pathogens N. meningitidis and S. pneumoniae. Routine use of these vaccines has resulted in decreased nasopharyngeal colonization, as well as infection. Currently approximately ˜25% of the global vaccine market comprises conjugated vaccines.
Gram-positive bacteria have a cell membrane that is surrounded by capsular polysaccharides. Staphylococcus is one such Gram-positive bacterium.
Staphylococcus aureus causes infection. S. aureus is an opportunistic bacterial pathogen responsible for a diverse spectrum of human diseases. Although S. aureus may colonize mucosal surfaces of normal humans, it is also a major cause of wound infections and has the invasive potential to induce severe infections, including osteomyelitis, endocarditis, and bacteremia with metastatic complications (Lowy, F. D. 1998. Staphylococcus aureus infections. New Engl J Med 339:520-32). S. aureus is one of the most common agents implicated in ventilator-associated pneumonia, and it is an important and emerging cause of community-acquired pneumonia, affecting previously healthy adults and children lacking predisposing risk factors (Kollef, M. H., A. Shorr, Y. P. Tabak, V. Gupta, L. Z. Liu, and R. S. Johannes. 2005. Epidemiology and outcomes of health-care-associated pneumonia: results from a large US database of culture-positive pneumonia. Chest 128:3854-62; Shorr, A. F. 2007. Epidemiology and economic impact of meticillin-resistant Staphylococcus aureus: review and analysis of the literature. Pharmacoeconomics 25:751-68).
S. aureus is the second most common cause of nosocomial bacteremia, and methicillin-resistant S. aureus (MRSA) strains account for more than 50% of all infections in intensive care units in the U.S. S. aureus infections within the hospital and in the community are increasing. MRSA strains were isolated from 2% of staphylococcal infections in 1974 and from 63% of staphylococcal infections in 2004. Many of the nosocomial MRSA strains are multi-drug resistant, and even methicillin-sensitive strains can be deadly. A recent report using population-based, active case finding revealed that 94,360 invasive MRSA infections occurred in the U.S. in 2005, and that the majority of these (58%) occurred outside of the hospital (Klevens, R. M., M. A. Morrison, J. Nadle, S. Petit, K. Gershman, S. Ray, L. H. Harrison, R. Lynfield, G. Dumyati, J. M. Townes, A. S. Craig, E. R. Zell, G. E. Fosheim, L. K. McDougal, R. B. Carey, and S. K. Fridkin. 2007. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA 298:1763-71). In this analysis, more Americans died from MRSA (>18,000 deaths) in 2005 than from AIDS.
S. aureus USA100, also known as the New York/Japan clone, is an MRSA strain that represents the predominant U.S. hospital-acquired MRSA strain (McDougal, L. K., C. D. Steward, G. E. Killgore, J. M. Chaitram, S. K. McAllister, and F. C. Tenover. 2003. Pulsed-field gel electrophoresis typing of oxacillin-resistant Staphylococcus aureus isolates from the United States: establishing a national database. J Clin Microbiol 41:5113-20).
Epidemiologic analyses indicate that S. aureus causes approximately 2 million clinical infections each year in the U.S. alone (Fridkin, S. K., J. C. Hageman, M. Morrison, L. T. Sanza, K. Como-Sabetti, J. A. Jernigan, K. Harriman, L. H. Harrison, R. Lynfield, and M. M. Farley. 2005. Methicillin-resistant Staphylococcus aureus disease in three communities. N Engl J Med 352:1436-44; King, M. D., B. J. Humphrey, Y. F. Wang, E. V. Kourbatova, S. M. Ray, and H. M. Blumberg. 2006. Emergence of community-acquired methicillin-resistant Staphylococcus aureus USA 300 clone as the predominant cause of skin and soft-tissue infections. Ann Intern Med 144:309-17; Klevens, R. M., M. A. Morrison, J. Nadle, S. Petit, K. Gershman, S. Ray, L. H. Harrison, R. Lynfield, G. Dumyati, J. M. Townes, A. S. Craig, E. R. Zell, G. E. Fosheim, L. K. McDougal, R. B. Carey, S. K. Fridkin, and M. I. for the Active Bacterial Core surveillance. 2007. Invasive methicillin-resistant Staphylococcus aureus infections in the United States. JAMA 298:1763-1771). Not only are S. aureus infections increasing in number, but the resistance of S. aureus to antibiotics is also on the increase. MRSA accounts for 40%-60% of nosocomial S. aureus infections in the U.S., and many of these strains are multi-drug resistant. Notorious as a major source of nosocomial infections, S. aureus has recently taken on a new role in causing an escalating number of community-acquired infections in non-hospitalized persons without predisposing risk factors. Virulent community-associated MRSA (CA-MRSA) strains are becoming more prevalent across the U.S. and Europe, and their dissemination has been observed globally (Baggett, H. C., T. W. Hennessy, K. Rudolph, D. Bruden, A. Reasonover, A. Parkinson, R. Sparks, R. M. Donlan, P. Martinez, K. Mongkolrattanothai, and J. C. Butler. 2004. Community-onset methicillin-resistant Staphylococcus aureus associated with antibiotic use and the cytotoxin Panton-Valentine leukocidin during a furunculosis outbreak in rural Alaska. J Infect Dis 189:1565-73; Gilbert, M., J. MacDonald, D. Gregson, J. Siushansian, K. Zhang, S. Elsayed, K. Laupland, T. Louie, K. Hope, M. Mulvey, J. Gillespie, D. Nielsen, V. Wheeler, M. Louie, A. Honish, G. Keays, and J. Conly. 2006. Outbreak in Alberta of community-acquired (USA300) methicillin-resistant Staphylococcus aureus in people with a history of drug use, homelessness or incarceration. Canad Med Assoc J 175:149-54; Kazakova, S. V., J. C. Hageman, M. Matava, A. Srinivasan, L. Phelan, B. Garfinkel, T. Boo, S. McAllister, J. Anderson, B. Jensen, D. Dodson, D. Lonsway, L. K. McDougal, M. Arduino, V. J. Fraser, G. Killgore, F. C. Tenover, S. Cody, and D. B. Jernigan. 2005. A clone of methicillin-resistant Staphylococcus aureus among professional football players. N Engl J Med 352:468-75).
Not only has S. aureus resistance to methicillin become more common, but numerous isolates with reduced susceptibility to vancomycin have been reported. Seven clinical isolates of S. aureus that carry vanA and are fully resistant to vancomycin have been isolated in the U.S. These isolates are also methicillin resistant (Chang, S., D. M. Sievert, J. C. Hageman, M. L. Boulton, F. C. Tenover, F. P. Downes, S. Shah, J. T. Rudrik, G. R. Pupp, W. J. Brown, D. Cardo, and S. K. Fridkin. 2003. Infection with vancomycin-resistant Staphylococcus aureus containing the vanA resistance gene. New Engl J Med 348:1342-7). Because S. aureus cannot always be controlled by antibiotics and MRSA isolates are becoming increasingly prevalent in the community, additional control strategies, such as a vaccine, are sorely needed.
S. aureus capsular polysaccharides are involved in infection. Many virulence factors contribute to the pathogenesis of staphylococcal infections, including surface-associated adhesions, secreted exoproteins and toxins, and immune evasion factors (Foster, T. J. 2005. Immune evasion by staphylococci. Nature Reviews Microbiology 3:948-58). Like many invasive bacterial pathogens, S. aureus produces a capsular polysaccharide (CP) (FIG. 4) that enhances its resistance to clearance by host innate immune defenses. Most clinical isolates of S. aureus are encapsulated, and serotype 5 and 8 strains predominate (Arbeit, R. D., W. W. Karakawa, W. F. Vann, and J. B. Robbins. 1984. Predominance of two newly described capsular polysaccharide types among clinical isolates of Staphylococcus aureus. Diagn Microbiol Infect Dis 2:85-91). The type 5 (CP5) and type 8 (CP8) capsular polysaccharides have similar trisaccharide repeating units comprised of N-acetyl mannosaminuronic acid (ManNAcA), N-acetyl L-fucosamine (L-FucNAc), and N-acetyl D-fucosamine (D-FucNAc) (Jones, C. 2005. Revised structures for the capsular polysaccharides from Staphylococcus aureus types 5 and 8, components of novel glycoconjugate vaccines. Carbohydr Res 340:1097-106). CP5 and CP8 are serologically distinct, and this can be attributed to differences in the linkages between the sugars and in the sites of O-acetylation (FIG. 4).
Previous studies have correlated S. aureus capsule production with resistance to in vitro phagocytic uptake and killing (Fattom, A., R. Schneerson, S. C. Szu, W. F. Vann, J. Shiloach, W. W. Karakawa, and J. B. Robbins. 1990. Synthesis and immunologic properties in mice of vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides conjugated to Pseudomonas aeruginosa exotoxin A. Infect Immun 58:2367-74; Thakker, M., J.-S. Park, V. Carey, and J. C. Lee. 1998. Staphylococcus aureus serotype 5 capsular polysaccharide is antiphagocytic and enhances bacterial virulence in a murine bacteremia model. Infect Immun 66:5183-5189; Watts, A., D. Ke, Q. Wang, A. Pillay, A. Nicholson-Weller, and J. C. Lee. 2005. Staphylococcus aureus strains that express serotype 5 or serotype 8 capsular polysaccharides differ in virulence. Infect Immun 73:3502-11). Human neutrophils phagocytose capsule-negative mutants in the presence of nonimmune serum with complement activity, whereas encapsulated isolates require both capsule-specific antibodies and complement for optimal opsonophagocytic killing (Bhasin, N., A. Albus, F. Michon, P. J. Livolsi, J.-S. Park, and J. C. Lee. 1998. Identification of a gene essential for O-acetylation of the Staphylococcus aureus type 5 capsular polysaccharide. Mol Microbiol 27:9-21; Thakker, M., J.-S. Park, V. Carey, and J. C. Lee. 1998. Staphylococcus aureus serotype 5 capsular polysaccharide is antiphagocytic and enhances bacterial virulence in a murine bacteremia model. Infect Immun 66:5183-5189; Watts, A., D. Ke, Q. Wang, A. Pillay, A. Nicholson-Weller, and J. C. Lee. 2005. Staphylococcus aureus strains that express serotype 5 or serotype 8 capsular polysaccharides differ in virulence. Infect Immun 73:3502-11). Nilsson et al. (Nilsson, I.-M., J. C. Lee, T. Bremell, C. Ryden, and A. Tarkowski. 1997. The role of staphylococcal polysaccharide microcapsule expression in septicemia and septic arthritis. Infect Immun 65:4216-4221) reported that peritoneal macrophages from mice phagocytosed significantly greater numbers of a CP5-negative mutant compared to the parental strain Reynolds. Once phagocytosed, the CP5-positive strain survived intracellularly to a greater extent than the mutant strain. Cunnion et al. (Cunnion, K. M., J. C. Lee, and M. M. Frank. 2001. Capsule production and growth phase influence binding of complement to Staphylococcus aureus. Infect Immun 69:6796-6803) compared opsonization of isogenic S. aureus strains and demonstrated that the CP5-positive strain bound 42% less serum complement (C′) than the acapsular mutant.
S. aureus vaccine development conventionally has involved the capsule as a target. Vaccine design for protection against staphylococcal disease is complicated by the protean manifestations and clinical complexity of S. aureus infections in humans. Many S. aureus vaccine candidates have been investigated in animal models of infection, but it has been reported that only two immunization regimens have completed phase III clinical trials (Schaffer, A. C., and J. C. Lee. 2008. Vaccination and passive immunisation against Staphylococcus aureus. Int J Antimicrob Agents 32 Suppl 1:S71-8). The first vaccine is based on the two capsular polysaccharides (CPs) (FIG. 4) that are most prevalent among clinical strains of S. aureus. Fattom et al. (Fattom, A. R. Schneerson, S. C. Szu, W. F. Vann, J. Shiloach, W. W. Karakawa and J. B. Robbins. 1990. Synthesis and immunologic properties in mice of vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides conjugated to Pseudomonas aeruginosa exotoxin. Infect Immun 58: 2367-74) conjugated the serotype 5 (CP5) and serotype 8 (CP8) polysaccharides to nontoxic recombinant P. aeruginosa exoprotein A (rEPA). The conjugate vaccines were immunogenic in mice and humans, and they induced opsonic antibodies that showed efficacy in protecting rodents from lethality and from nonlethal staphylococcal infection (Fattom, A. R. Schneerson, S. C. Szu, W. F. Vann, J. Shiloach, W. W. Karakawa and J. B. Robbins. 1990. Synthesis and immunologic properties in mice of vaccines composed of Staphylococcus aureus type 5 and type 8 capsular polysaccharides conjugated to Pseudomonas aeruginosa exotoxin. Infect Immun 58: 2367-74; Fattom, A., R. Schneerson, D. C. Watson, W. W. Karakawa, D. Fitzgerald, I. Pastan, X. Li, J. Shiloach, D. A. Bryla, and J. B. Robbins. 1993. Laboratory and clinical evaluation of conjugate vaccines composed of S. aureus type 5 and type 8 capsular polysaccharides bound to Pseudomonas aeruginosa recombinant exoprotein A. Infect Immun 61:1023-32; Fattom, A. I., J. Sarwar, A. Ortiz, and R. Naso. 1996. A Staphylococcus aureus capsular polysaccharide (CP) vaccine and CP-specific antibodies protect mice against bacterial challenge. Infect Immun 64:1659-65; Lee, J. C., J. S. Park, S. E. Shepherd, V. Carey, and A. Fattom. 1997. Protective efficacy of antibodies to the Staphylococcus aureus type 5 capsular polysaccharide in a modified model of endocarditis in rats. Infect Immun 65:4146-51). Passive immunization studies have indicated that both CP5- and CP8-specific antibodies significantly reduce infection in a murine model of S. aureus mastitis (Tuchscherr, L. P., F. R. Buzzola, L. P. Alvarez, J. C. Lee, and D. O. Sordelli. 2008. Antibodies to capsular polysaccharide and clumping factor A prevent mastitis and the emergence of unencapsulated and small-colony variants of Staphylococcus aureus in mice. Infect Immun 76:5738-44). The combined CP5- and CP8-conjugate vaccine was shown to be safe in humans and elicited antibodies that showed opsonophagocytic activity.
S. aureus vaccine development has also involved surface proteins as a target. The second S. aureus clinical vaccine trial was based on the protective efficacy of antibodies to staphylococcal adhesions in preventing staphylococcal infections. S. aureus clumping factor A is a cell wall-anchored protein that is surface expressed, mediates staphylococcal adherence to fibrinogen (Foster, T. J., and M. Hook. 1998. Surface protein adhesins of Staphylococcus aureus. Trends Microbiol 6:484-8), and promotes the attachment of S. aureus to biomaterial surfaces (Vaudaux, P. E., P. Francois, R. A. Proctor, D. McDevitt, T. J. Foster, R. M. Albrecht, D. P. Lew, H. Wabers, and S. L. Cooper. 1995. Use of adhesion-defective mutants of Staphylococcus aureus to define the role of specific plasma proteins in promoting bacterial adhesion to canine arteriovenous shunts. Infection & Immunity 63:585-90), blood clots, and damaged endothelial surfaces (Moreillon, P., J. M. Entenza, P. Francioli, D. McDevitt, T. J. Foster, P. Francois, and P. Vaudaux. 1995. Role of Staphylococcus aureus coagulase and clumping factor in pathogenesis of experimental endocarditis. Infection & Immunity 63:4738-43). The fibrinogen-binding domain of ClfA is located within region A of the full-length protein (McDevitt, D., P. Francois, P. Vaudaux, and T. J. Foster. 1995. Identification of the ligand-binding domain of the surface-located fibrinogen receptor (clumping factor) of Staphylococcus aureus. Molecular Microbiology 16:895-907). ClfA plays an important role in S. aureus binding to platelets, an interaction that is critical in animal models of catheter-induced staphylococcal endocarditis (Sullam, P. M., A. S. Bayer, W. M. Foss, and A. L. Cheung. 1996. Diminished platelet binding in vitro by Staphylococcus aureus is associated with reduced virulence in a rabbit model of infective endocarditis. Infection & Immunity 64:4915-21).
Nanra et al. reported that antibodies to ClfA induced opsonophagocytic killing of S. aureus in vitro (Nanra, J. S., Y. Timofeyeva, S. M. Buitrago, B. R. Sellman, D. A. Dilts, P. Fink, L. Nunez, M. Hagen, Y. V. Matsuka, T. Mininni, D. Zhu, V. Pavliak, B. A. Green, K. U. Jansen, and A. S. Anderson. 2009. Heterogeneous in vivo expression of clumping factor A and capsular polysaccharide by Staphylococcus aureus: Implications for vaccine design. Vaccine 27:3276-80). Furthermore, mice immunized with a recombinant form of the binding region A of ClfA showed reductions in arthritis and lethality induced by S. aureus (Josefsson, E., O. Hartford, L. O'Brien, J. M. Patti, and T. Foster. 2001. Protection against experimental Staphylococcus aureus arthritis by vaccination with clumping factor A, a novel virulence determinant. Journal of Infectious Diseases 184:1572-80). Passive immunization experiments were performed in rabbits given a human polyclonal immunoglobulin preparation that contained elevated levels of antibodies specific for ClfA (Vernachio, J., A. S. Bayer, T. Le, Y. L. Chai, B. Prater, A. Schneider, B. Ames, P. Syribeys, J. Robbins, J. M. Patti, J. Vernachio, A. S. Bayer, T. Le, Y.-L. Chai, B. Prater, A. Schneider, B. Ames, P. Syribeys, J. Robbins, and J. M. Patti. 2003. Anti-clumping factor A immunoglobulin reduces the duration of methicillin-resistant Staphylococcus aureus bacteremia in an experimental model of infective endocarditis. Antimicrobial Agents & Chemotherapy 47:3400-6). The combination therapy resulted in better bacterial clearance from the blood of rabbits with catheter-induced S. aureus endocarditis than did vancomycin treatment alone. In addition, passive transfer of ClfA-specific antibodies significantly reduced infection in a murine model of S. aureus mastitis (Tuchscherr, L. P., F. R. Buzzola, L. P. Alvarez, J. C. Lee, and D. O. Sordelli. 2008. Antibodies to capsular polysaccharide and clumping factor A prevent mastitis and the emergence of unencapsulated and small-colony variants of Staphylococcus aureus in mice. Infect Immun 76: 5738-44).
A phase III clinical trial was reportedly designed to protect against late-onset sepsis in 2000 low birth weight, premature neonates. The infants received up to four administrations of Veronate, a human immunoglobulin preparation pooled from donors with elevated antibody titers against ClfA and SdrG. Despite the promising results from a similar phase II clinical trial, this prophylactic therapy resulted in no reduction in the frequency of staphylococcal infections in the neonates (DeJonge, M., D. Burchfield, B. Bloom, M. Duenas, W. Walker, M. Polak, E. Jung, D. Millard, R. Schelonka, F. Eyal, A. Morris, B. Kapik, D. Roberson, K. Kesler, J. Patti, and S. Hetherington. 2007. Clinical trial of safety and efficacy of INH-A21 for the prevention of nosocomial staphylococcal bloodstream infection in premature infants. J Pediatr 151:260-5).
It has been shown that protein glycosylation occurs, but rarely does so naturally, in prokaryotic organisms. On the other hand, N-linked protein glycosylation is an essential and conserved process occurring in the endoplasmic reticulum of eukaryotic organisms. It is important for protein folding, oligomerization, stability, quality control, sorting and transport of secretory and membrane proteins (Helenius, A., and Aebi, M. (2004). Roles of N-linked glycans in the endoplasmic reticulum. Annu. Rev. Biochem. 73, 1019-1049). Protein glycosylation has a profoundly favorable influence on the antigenicity, the stability and the half-life of a protein. In addition, glycosylation can assist the purification of proteins by chromatography, e.g. affinity chromatography with lectin ligands bound to a solid phase interacting with glycosylated moieties of the protein. It is therefore established practice to produce many glycosylated proteins recombinantly in eukaryotic cells to provide biologically and pharmaceutically useful glycosylation patterns.
Conjugate vaccines have been successfully used to protect against bacterial infections. The conjugation of an antigenic polysaccharide to a protein carrier is required for protective memory response, as polysaccharides are T-cell independent antigens. Polysaccharides have been conjugated to protein carriers by different chemical methods, using activation reactive groups in the polysaccharide as well as the protein carrier. (Qian, F., Y. Wu, O. Muratova, H. Zhou, G. Dobrescu, P. Duggan, L. Lynn, G. Song, Y. Zhang, K. Reiter, N. MacDonald, D. L. Narum, C. A. Long, L. H. Miller, A. Saul, and G. E. Mullen. 2007. Conjugating recombinant proteins to Pseudomonas aeruginosa ExoProtein A: a strategy for enhancing immunogenicity of malaria vaccine candidates. Vaccine 25:3923-3933; Pawlowski, A., G. Kallenius, and S. B. Svenson. 2000. Preparation of pneumococcal capsular polysaccharide-protein conjugates vaccines utilizing new fragmentation and conjugation technologies. Vaccine 18:1873-1885; Robbins, J. B., J. Kubler-Kielb, E. Vinogradov, C. Mocca, V. Pozsgay, J. Shiloach, and R. Schneerson. 2009. Synthesis, characterization, and immunogenicity in mice of Shigella sonnei O-specific oligosaccharide-core-protein conjugates. Proc Natl Acad Sci USA 106:7974-7978).
Conjugate vaccines can be administered to children to protect them against bacterial infections and can provide a long lasting immune response to adults. Constructs of the invention have been found to generate an IgG response in animals. It is believed that the polysaccharide (i.e. sugar residue) triggers a short-term immune response that is sugar-specific. Indeed, the human immune system generates a strong response to specific polysaccharide surface structures of bacteria, such as O-antigens and capsular polysaccharides. However, as the immune response to polysaccharides is IgM dependent, the immune system develops no memory. The protein carrier that carries the polysaccharide, however, triggers an IgG response that is T-cell dependent and that provides long lasting protection since the immune system develops memory. For this reason, in developing a vaccine, it is advantageous to develop it as a protein carrier-polysaccharide conjugate.
Prokaryotic organisms rarely produce glycosylated proteins. However, it has been demonstrated that a bacterium, the food-borne pathogen Campylobacter jejuni, can glycosylate its proteins (Szymanski, et al. (1999). Evidence for a system of general protein glycosylation in Campylobacter jejuni. Mol. Microbiol. 32, 1022-1030). The machinery required for glycosylation is encoded by 12 genes that are clustered in the pgl locus. Disruption of glycosylation affects invasion and pathogenesis of C. jejuni but is not lethal as in most eukaryotic organisms (Burda P. and M. Aebi, (1999). The dolichol pathway of N-linked glycosylation. Biochim Biophys Acta 1426(2):239-57). It has been shown that the pgl locus is responsible for N-linked protein glycosylation in Campylobacter and that it is possible to reconstitute the N-glycosylation of C. jejuni proteins by recombinantly expressing the pgl locus and acceptor glycoprotein in E. coli at the same time (Wacker, M., D. Linton, P. G. Hitchen, M. Nita-Lazar, S. M. Haslam, S. J. North, M. Panico, H. R. Morris, A. Dell, B. W. Wren, and M. Aebi. 2002. N-linked glycosylation in C. jejuni and its functional transfer into E. coli. Science 298:1790-3).
The N-linked protein glycosylation biosynthetic pathway of Campylobacter has significant similarities to the polysaccharide biosynthesis pathway in bacteria (Bugg, T. D., and P. E. Brandish. 1994. From peptidoglycan to glycoproteins: common features of lipid-linked oligosaccharide biosynthesis. FEMS Microbiol Lett 119:255-62). Based on the knowledge that antigenic polysaccharides of bacteria and the oligosaccharides of Campylobacter are both synthesized on the carrier lipid, undecaprenyl pyrophosphate (UndPP), the two pathways were combined in E. coli (Feldman, M. F., M. Wacker, M. Hernandez, P. G. Hitchen, C. L. Marolda, M. Kowarik, H. R. Morris, A. Dell, M. A. Valvano, and M. Aebi. 2005. Engineering N-linked protein glycosylation with diverse O antigen lipopolysaccharide structures in Escherichia coli. Proc Natl Acad Sci USA 102:3016-21). It was demonstrated that PglB does not have a strict specificity for the lipid-linked sugar substrate. The antigenic polysaccharides assembled on UndPP are captured by PglB in the periplasm and transferred to a protein carrier (Feldman, M. F., M. Wacker, M. Hernandez, P. G. Hitchen, C. L. Marolda, M. Kowarik, H. R. Morris, A. Dell, M. A. Valvano, and M. Aebi. 2005. Engineering N-linked protein glycosylation with diverse O antigen lipopolysaccharide structures in Escherichia coli. Proc Natl Acad Sci USA 102:3016-21; Wacker, M., M. F. Feldman, N. Callewaert, M. Kowarik, B. R. Clarke, N. L. Pohl, M. Hernandez, E. D. Vines, M. A. Valvano, C. Whitfield, and M. Aebi. 2006. Substrate specificity of bacterial oligosaccharyltransferase (OTase) suggests a common transfer mechanism for the bacterial and eukaryotic systems. Proc Natl Acad Sci USA 103:7088-93). It was shown that Campylobacter PglB transfers a diverse array of UndPP linked oligosaccharides if they contain an N-acetylated hexosamine at the reducing terminus (Wacker et al. (2006)), allowing conjugation of an antigenic polysaccharide to a protein of choice through an N-glycosidic linkage. While this may provide a theoretical basis for production of conjugated vaccines in vivo, many difficult challenges need to be overcome in order to realize this theoretical possibility.
Based on this previous discovery that C. jejuni contains a general N-linked protein glycosylation system, E. coli had been modified to include the N-linked protein glycosylation machinery of C. jejuni. In this way, glycosylated forms of proteins native to C. jejuni in an E. coli host were produced. It had been further shown that this process could be used to produce glycosylated proteins from different origins in modified E. coli host for use as vaccine products. Production by E. coli is advantageous because large cultures of such modified E. coli hosts can be produced which produce large quantities of useful vaccine.
Using this process to produce a glycosylated protein in a modified E. coli host for use as a vaccine product for S. aureus encounters problems that have been perceived to be insurmountable. First, E. coli is a Gram-negative bacterium and its saccharide biosynthesis pathways differ greatly from those of a Gram-positive bacterium, such as S. aureus, after the polymerization step. In addition, it would have been infeasible to genetically engineer E. coli to produce the S. aureus capsular polysaccharide directly consistent with previous technologies. For example, S. aureus is a Gram positive organism and its capsule synthesis is associated with cell envelope structure and construction of the cellular hull. The capsule producing biosynthetic machinery is specifically designed to arrange the capsular polysaccharide (PS) on the outside of the cell and its cell wall. It would have been extremely difficult, for at least the reason that it would be highly resource-intensive, to produce this capsule in a modified E. coli organism, because the cell envelope of E. coli is constructed in a fundamentally different way. The biosynthetic machinery for capsule assembly from PS precursor would be non-functional due to the different environment. Whereas the S. aureus capsule must transit a single membrane, in E. coli there is an additional membrane which needs to be crossed to reach the final location of an authentic capsule. Furthermore, as the S. aureus capsule is very large, it was believed to be infeasible to make a large capsule like the S. aureus capsule between the two membranes of E. coli. 
The principle that enzymes from different organisms can work together has been shown before (e.g. Rubires, X., F. Saigi, N. Pique, N. Climent, S. Merino, S. Alberti, J. M. Tomas and M. Regue. 1997. A gene (wbbL) from Serratia marcescens N28b (04) complements the rfb-50 mutation of Escherichia coli K-12 derivatives. J. Bacteriol 179(23): 7581-6). However, it is believed that no modified LPS polysaccharide from a Gram-positive organism has previously been produced in a Gram-negative organism.